\documentclass[tikz,border=10pt]{standalone}
\usepackage{tikz}
\usetikzlibrary{positioning}
\usepackage{tikz-feynman}
\begin{document}

\begin{tikzpicture}
    \begin{feynman}
        %% fig h
        \vertex (h1) at (0,0);
        \vertex[right =1cm  of h1] (h2);
        \vertex[right =2cm  of h1, anchor=center] (h3){};
        \vertex[right =3cm  of h1] (h4);
        \vertex[right =4cm  of h1] (h5);
        \vertex[above =-1.4cm  of h3] (h6);
        \node[above =0.5cm  of h5] {};
        % 对各个顶点连线
        \diagram*{
            { [edge= fermion]
                    (h1) --  (h3)--(h5),
                },
            % 介子连线
            % { [edge= charged scalar]
            % (h3) --[half left ](h6)--[half left](h3),
            % }
        };
        \draw  (h3) edge [anti charged scalar,loop, min distance=3.5cm] (h3);
        % 画 magnet 顶点
        \node at (h3) [draw,fill=black!20,shape=rectangle,minimum size=10] {};
    \end{feynman}

\end{tikzpicture}


\end{document}
